public class Pillar {
     	Geometry  bottom;        //bottom是抽象类Geometry声明的变量
  	double height;
     	Pillar (Geometry bottom,double height) {
      		this.bottom=bottom; 
     		this.height=height;
 	}
  	public double getVolume() {
	 	if(bottom==null) {
	      		System.out.println("没有底,无法计算体积");
	    		return -1;
    		}
	 	return bottom.getArea()*height; //bottom可以调用子类重写的getArea方法
    	}
}




